Device-to-device (D2D) communication between devices may take place after D2D-capable devices are made aware of the presence of other peer devices in their vicinity, and of the services that those devices offer and/or participate in. The discovery process may be viewed as distinct from the data communication process itself. From the radio perspective, it is possible that the device discovery may happen in a different frequency, as compared to the communication, (in this case, the judgment of the quality of the D2D link in the discovery frequency may have to be translated into a judgment of the corresponding D2D data link frequencies). One may envision discovery over a physical link between the devices, followed by communication over a local path that does not involve a direct physical D2D link.
Direct D2D communications are gaining importance lately. This requires a change in the current third generation partnership project (3GPP) architecture with the addition of new nodes and interfaces. An architecture that facilitates the coordination of D2D communication from within the operator network or by third party applications outside the 3GPP network is needed. Once service discovery is complete, procedures for call establishment and maintenance are needed for both unicast and multicast/broadcast D2D sessions. Service discovery and call establishment procedures are also needed to enable inter-operator D2D communications in order for D2D services to pick up momentum in the market.